Fluid swivel stacks are known in the art for transfer of high-pressure fluids across multiple rotary interfaces between an incoming fluid line and an outgoing product piping, i.e., one rotary interface per swivel in the swivel stack. Applications for such a swivel stack include for example offshore oil and gas explorations where high-pressure flows of oil and/or gas are transferred from a (deep-sea) offshore well to a floating vessel such as a Floating Production Storage and Offloading (FPSO) vessel. Typically, such a floating vessel is equipped with a turret mooring system that can couple a mooring buoy or a “mooring structure” holding one or more riser lines from the well, to product piping ducts on the vessel. Since the vessel can weathervane in its moored position, the turret mooring system should allow some rotation between the vessel and the buoy. The swivel stack is likewise adapted to provide rotation between the incoming fluid line and the product piping in each swivel of the stack.
It has been observed that the number of incoming flow lines from a production to the FPSO vessel tends to increase to allow an increase of the throughput from the well to the FPSO. This causes the swivel stack to become more complex as more incoming flow lines need to be accommodated in the turret, mainly by increasing the number of swivels in the swivel stack. As a result, the height of the swivel stack increases. Also the diameter of the swivel stack needs to be enlarged as more incoming flow lines are assembled in the swivel stack. It will be understood that the weight of the stack also increases which requires the use of reinforcements in the construction of the turret and the swivel stack.
Moreover, the increased complexity poses some demands with respect to access, maintenance, repair, and operation that should remain feasible and straightforward. This contributes also to a design of a swivel stack that is large, tall and heavy. For instance, sufficient spacing shall be ensured between consecutive units to allow access in view of local dismantling of the unit being repaired for seal replacement.
It is an object of the present invention to overcome or mitigate one or more of these disadvantages from the prior art.